FIG 3.
Effects of different external pyruvate concentrations on PyhjX-gfp activation at the single-cell level. E. coli cells expressing gfp under the control of the PyhjX promoter were grown in M9 minimal medium containing increasing concentrations of pyruvate (supplemented with succinate; final carbon concentration, 20 mM) and analyzed by fluorescence microscopy. A total of 200 cells was analyzed in each experiment at the time point of maximal expression, and frequency refers to the percentage of cells with the indicated intensity (see Materials and Methods). Histograms of the fluorescence intensities of cells were fitted using a Gaussian distribution (solid line). The dashed line represents the threshold of activation for the reporter strain. AU, arbitrary units. Experiments were performed independently three times.